The present invention relates to a combustion apparatus having improved airflow, and more specifically to a multiple-chamber combustion apparatus having improved airflow through the apparatus, as used in conjunction with combustion-powered fastener driving tools.
Gas combustion devices are known in the art. A practical application of this technology is found in combustion-powered fastener driving tools. One type of such tools, also known as IMPULSE® brand tools for use in driving fasteners into workpieces, is described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162, 4,483,473, 4,483,474, 4,403,722, 5,197,646, and 5,263,439, all of which are incorporated by reference herein. Similar combustion powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE® brand, and from ITW-S.P.I.T. of Bourg-les-Valence, France under the PULSA® brand.
Such tools incorporate a generally pistol-shaped tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. Such ancillary processes include: inserting the fuel into the combustion chamber; mixing the fuel and air within the chamber; and removing, or purging, combustion by-products. In addition to these ancillary processes, the fan further serves to cool the tool and increase combustion energy output.
The combustion engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a cylinder body. A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when a work contact element at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel metering valve to introduce a specified volume of fuel into the closed combustion chamber.
A trigger switch is pulled, which causes the spark to ignite a charge of gas in the combustion chamber of the engine. Upon ignition of the combustible fuel/air mixture, the combustion in the chamber causes the acceleration of the piston/driver blade assembly, which shoots downward to impact a positioned fastener and drive the fastener into the workpiece if the fastener is present. The piston then returns to its original, or “ready” position, through differential gas pressures within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
Single-chamber combustion apparatuses are effective in achieving a fast combustion cycle time. Single-chamber apparatuses are also efficient for executing the ancillary processes described above, particularly mixing air and fuel within the single chamber and purging combustion by-products. Single-chamber apparatuses, however, do not generally realize peak combustion pressures as high as those seen in other gas combustion-powered tools.
Two or more-chambered combustion tools are also known. These tools can yield significantly higher combustion pressures, and therefore more combustion energy, over a single-chambered apparatus. Multiple-chambered tools typically have a first chamber connected to a second chamber. The first chamber often has a tubular shape, but can be a variety of shapes as are known in the art. An ignition source, which is typically a spark plug, is located in, or in operable relationship to, the first chamber. One end of the first chamber is also in communication with the second chamber via a port or other opening allowing communication between the chambers. The port connecting the two chambers typically includes a reed valve, which remains normally closed to prevent back flow of pressure from the second chamber into the first chamber.
A fuel/air mixture in the first chamber is ignited at one closed end of the first chamber, and advances a flame front toward another end of the chamber having the port. As the flame front advances, unburned fuel/air ahead of the flame front is pushed into the second chamber, thereby compressing the fuel/air mixture in the second chamber. As the flame propagates through the port and reed valve, the air/fuel mixture in the second chamber also ignites. This ignited gas thus rapidly builds pressure within the second chamber, and closes the reed valve to prevent loss of pressure back into the first chamber. The greater the compression in the second chamber, the greater will be the final combustion pressure of the tool, which is desirable. The combustion pressure is further increased as the path for the ignited gas to travel through the port between the first and second chambers is made more restrictive.
A restrictive path between the two chambers, however, makes it difficult to communicate the air/fuel mixture from the first chamber into the second chamber in a short amount of time. Multiple-chambered tools, therefore, typically provide fuel distribution to both chambers separately through a common fuel supply line with two orifices. Such configurations though, tend to increase the complexity and cost of the tool, which are undesirable. The restricted flow between both chambers also decreases the tool's ability to purge combustion by-products from both chambers, while inhibiting the tool's ability to fill the chambers with fresh air from outside of the tool, prior to injecting fuel to the chambers. Build-up of combustion by-products within the tool's chambers can decrease the tool's ability to realize consistent and repeatable combustion cycles. Alternatively, the restricted airflow between the two chambers requires additional time both to mix fuel within the chambers and to purge the chambers between combustion events. This extra time can be unfavorably noticeable to a tool operator while the tool is in use.
Accordingly, it is desirable to achieve an efficient airflow from one chamber to another in a multiple-chamber combustion tool apparatus, without sacrificing the increased combustion power resulting from use of a restrictive path between chambers, and without having to employ more than one fuel line in the apparatus.